Stop or move: Defensive strategies in humans

Area of Science:

• Psychology
• Neuroscience
• Human Behavior

Background:

• Threatening cues and environmental context elicit distinct defensive behaviors.
• Human defensive immobility is characterized by reduced body sway, with attentive immobility showing bradycardia and tonic immobility showing tachycardia.

Purpose of the Study:

• To investigate human defensive strategies in response to varying escape route availability.
• To differentiate between flight and immobility responses under different threat scenarios.

Main Methods:

• Participants were exposed to images of a man with a gun, varying in perceived escape possibility (gun directed away vs. toward observer).
• Control images used a non-lethal object instead of a gun.
• Posturography and electrocardiography were used to record body sway and heart rate.

Main Results:

• Higher amplitude of sway and heart rate were observed for images with greater escape possibility (gun directed away).
• Lower amplitude of sway and heart rate (bradycardia) were recorded for images with less escape possibility (gun directed toward).
• Compared to controls, gun-away images increased sway, while gun-toward images reduced sway and heart rate.

Conclusions:

• Humans exhibit active escape-like responses when threat allows for potential escape.
• When escape is perceived as blocked, humans display immobility with bradycardia, mirroring defensive strategies in other species.